System Requirements Document
One of the challenges we’ve encountered during the planning stages of cubesat development was that the project had exponentially increased in complexity. There are currently seven major departments, each responsible for their own components, testing protocols, deadlines, and points of contact. As the scope of the project expanded, so did the risk of misalignment, duplication of work, lack of documentation, and miscommunication across teams
To address this, Systems Engineering created the Systems Requirements Document (SRD). The SRD is a formal document that outlines the full set of functional, performance, interface, and design constraints that the satellite must satisfy. Primarily it serves to break down high-level mission objectives into detailed technical requirements across subsystems.
Creating the SRD was a collaborative and iterative process. We worked closely with leads and engineers from each department to identify key requirements, define subsystem responsibilities, and document critical interdependencies. In developing the document, we emphasized three core principles: Traceability, Clarity, and Verification.
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Traceability ensures that every requirement can be directly linked to a high-level mission objective.
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Clarity means presenting information in a standardized, easy-to-follow format that can be quickly understood and reused by any department.
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Verification outlines how each requirement will be tested, validated, or demonstrated, making it actionable throughout the lifecycle of the project.
For example, we collaborated with both the Radio Frequency Ground Station (RFGS) and Optical Ground Station (OGS) teams to create the requirements for mission-critical ground control software. This involved identifying shared interfaces, timing constraints, and command routing protocols that ensure seamless communication between the satellite and ground systems. Additionally, our SRD serves to create an organized framework for prioritizing the readiness of our systems by organizing them into parent requirement lists, where each requirement can be traced to a mission pre-requisite.
Example Requirement: OGS-15 Optical Ground Station in SRD
Requirement OGS-15 states that "The OGS shall be capable of detecting the downlink laser transmission at a link margin of 3 dB ≤ Margin ≤ 6 dB." We first ensured the statement was measurable by including margins in dB that give us a clear pass/fail criterion.
Then, we categorized the requirement level as Performance. The margin range comes directly from our Optical Tx Link Budget, which models the received power and losses under both nominal and degraded conditions. We chose 3–6 dB to ensure the link stays robust in the face of atmospheric attenuation, pointing errors, and optical losses, while also not over-specifying the system beyond practical limits.
For the Parent Requirements, we linked to OGS-09 (functional) and OGS-12 (performance) because both have to be met for OGS-15 to even make sense. OGS-09 covers the actual ability to detect downlink wave packets by polarization state — without that, margin is meaningless. OGS-12 sets the bit error rate range, which directly depends on having enough link margin; if the margin is too low, BER will climb above our limit.
We set the Verification Method to Analysis because we’ll be using link budget calculations to prove compliance, not an early physical demo. Running the numbers lets us confirm before hardware build that the optical chain can meet the 3–6 dB requirement.
Finally, the Compliance Timeline is CDR because that’s when we need to be sure the design will meet the required margin before we commit to fabrication.
By integrating these interdependent needs into the SRD early, we reduced the risk of downstream integration issues and clarified cross-team responsibilities. The SRD also plays a central role in design reviews, helping us to evaluate whether subsystem-level designs align with system-level goals. Now, other departments actively rely on the SRD as both a reference tool and a roadmap as they plan out their day to day assignments.